GLYCOL REGENERATION PROCESS AND EQUIPMENT

THE GLYCOL REBOILER

The glycol regeneration process is very important to maintain the correct concentration of the lean glycol. Refer to Figures: 50 & 52 for the equipment used in the Glycol Regeneration Process.

The glycol reboiler is the main piece of equipment that plays this role in the regeneration process. The reboiler supplies heat to separate the glycol and water by a simple distillation process.

The system consists of a ' U ' shaped, combustion chamber with gas burners, set into the shell of the reboiler and includes an outlet stack for the waste combustion gases.

The shell also contains a ' Weir ' that maintains the level of glycol above the fire-tube in order to prevent overheating of the tube and subsequent damage and/or glycol decomposition by excess heat.

Figure: 32 - Fire-tube Reboiler

The temperature of the reboiler should be in the range of 375 to 390 °F. This temperature will usually give good distillation of the rich glycol and evaporate all water out of it.

The glycol should never be heated above 400 °F as it begins to decompose above that temperature.

Note: When making adjustments to reboiler temperature, never increase the temperature setting by more than five degrees at a time.

Too great an increase will cause the control system to open the fuel gas valve too wide, giving a large burner flame which in turn will cause flame impingement on the inside of the fire-tube. This will lead to ' Hot-spots ' and cause damage to the fire-tube and breakdown of the glycol into corrosive organic acids.

If coke , salts or tar deposits form on the fire tube, the heat transfer into the glycol is reduced, the control system will increase the fuel to maintain the glycol temperature and tube failure can result. Localised overheating, especially where salt deposits accumulate, will decompose the glycol.

Salt deposits can be detected by shutting off the burner on the glycol reboiler system at night and looking down the fire-box. A bright red glow will be visible at the hot spots on the fire tube walls where salt deposits have collected. An analysis of the glycol will determine the degree of the contamination.

It is highly recommended that, during a plant start-up, make sure the reboiler is up to the desired operating temperature before flowing gas through the contactor .

Some fires have been caused by leaks in the gas lines near the fire-box. The best precaution is to have valves and regulators in the gas line at a suitable distance from the firebox.

Another very effective measure is the addition of a flame arrestor around the fire-box. If the flame arrestor is properly designed, even severe gas leaks in the immediate vicinity of the fire-box will not ignite.